Abbreviations
3GPP 3rd generation partnership project
AC Access Class
ACB Access Class Barring
AS Access Stratum
E-UTRAN Evolved UTRAN
eNodeB, eNB Evolved NodeB
EAB Extended Access Barring
EDGE Enhanced Data Rates for GSM Evolution
GERAN GSM Edge RAN
GSM Global system for mobile communication
IE Information element
MME Mobility Management Entity
MMEGI MME group identity
MMEC MME code
MTC Machine Type Communication
NAS Non Access Stratum
PLMN Public Land Mobile Network
RAN Radio Access Network
RRC radio resource control
SIB System Information Block
UE User equipment (same as terminal)
UL UpLink
UTRAN Universal Terrestrial Radio Access Network
The present application is related to extended access barring (EAB). 3GPP is discussing EAB as a mean to bar the UEs in overload situations. The requirements are captured in 3GPP TS 22.011 V11.0.0. (chapter 4.3.4).
EAB should be applied depending on the category where UE belongs to and this category is up to the PLMN registration situation as following;                a) UEs that are configured for EAB;        b) UEs that are configured for EAB and are neither in their HPLMN nor in a PLMN that is equivalent to it;        c) UEs that are configured for EAB and are neither in the PLMN listed as most preferred PLMN of the country where the UE is roaming in the operator-defined PLMN selector list on the SIM/USIM, nor in their HPLMN nor in a PLMN that is equivalent to their HPLMN.        
Above categories are designed as many MTC devices are roamers.
For instance, in some MTC application, MTC devices are using roamer SIM/USIM with preferred PLMN. That means Operator-A in country-1 gives Operator-A's SIM card of country-2 to its MTC devices in country-1. So all the MTC devices are actually roamers in country-1 but PLMN of Operator-A in country-1 will be the most preferred PLMN. Thus above category is important to bar separately between all the roamers (b) and roamers which are not in the most preferred PLMN(c). In the above example, if Operator-B's network node, which is serving the same area as Operator-A's network node, is breaking down, all Operator-B's MTC devices will try to roam to Operator-A's system and this will cause overload to Operator-A as well. However if there is no separation of category c) from b), network bars all roamer with b), Operator-A's own MTC devices cannot be served either. Thus in this case, category c) barring can be used only to bar the Operator-B's MTC devices.
However, in case that network sharing is used in the network, it is not clear how EAB should be applied and how EAB related parameters should be broadcast. If the E-UTRAN is shared by multiple operators, the system information broadcasted in each shared cell contains the PLMN-id of each operator (according to current specifications up to 6 PLMN-ids), i.e. PLMN-IdentityList as in FIG. 8. The UE shall read up the PLMN-ids to select one of the PLMN-ids during PLMN selection procedure and to indicate this PLMN-id to the E-UTRAN via RRC Connection Setup Complete message. The E-UTRAN then selects an appropriate MME for the PLMN indicated by the UE.
FIG. 8 explains parameters related to network sharing in pseudo-code language.
In case the network broadcasts multiple PLMN_IDs, UE AS layer will forward them to NAS layer and NAS layer will select one. And NAS layer will indicate this selected PLMN to AS layer and AS layer will include it in the corresponding RRCConnection Setup Complete message as shown in FIG. 9.
Basically, the content of the RRCConnectionSetupComplete message is set as follows:
1> set the content of RRCConnectionSetupComplete message as follows:2>set the selectedPLMN-Identity to the PLMN selectedby upper layers (see TS 23.122, TS 24.301) from the PLMN(s)included in the plmn-IdentityList inSystemInformationBlockType1;2>if upper layers provide the ‘Registered MME’,include and set the registeredMME as follows:3>if the PLMN identity of the ‘Registered MME’ isdifferent from the PLMN selected by the upper layers:4>include the plmnIdentity in theregisteredMME and set it to the value of thePLMN identity in the ‘Registered MME’ receivedfrom upper layers;3> set the mmegi and the mmec to the value received fromupper layers;
Combining network sharing and overload situation generates more cases to consider.
For instance, Operator-A and Operator-B are sharing the RAN node in country 1 as shown in FIG. 1. And Operator-C is serving the same area as Operators A and B but has his own RAN system. And Operator-A and Operator-B have own MTC customers but have different business models. Operator-A's MTC devices have Operator-A's Country-2 SIM/USIM (i.e, they are roamers in country 1), while Operator-B's MTC devices have Operator-B's Country-1 SIM/USIM (i.e., they are in their home network). And in case MME3 is broken, MTC devices of Operator-3 will try to roam to Operator-A/B's network which may cause overload. Thus EAB has to be set in eNB-a to prevent serving Operator-3's MTC devices while eNB-a still serves MTC devices of Operator-A/B as normal.
PLMN selection of Operator-C's MTC devices may vary depending on the settings of devices and the policy of Operator-C. They may select either PLMN1 or PLMN2. From Operator-A's point of view, Operator-C's MTC devices belong to category c) while from Operator-B's point of view Operator-C's MTC devices belong to category b). Thus with the current solution, if category b) is set for EAB in eNB-a, MTC devices of Operator-A will be also barred. If category c) is set for EAB in eNB-a and PLMN2 is configured as preferred PLMN in Operator-C's MTC devices, Operator-C's MTC devices will be served if they select PLMN2.
Even though EAB is invented to prevent RAN overload, the same mechanism may be used for Core network overload mitigation. In this example, MTC business model is the same as the above. (i.e., Operator-A's MTC has roamers' SIM/USIM while Operator-B's MTC has home SIM/USIM)
As in FIG. 2, in case MME2 is heavily loaded, eNB will want to bar the MTC devices of Operator-B while Operator-A's MTC devices can be served normally. However if the category for the EAB is common for all PLMN in network sharing, eNB will not be able to bar only Operator-B's MTC devices as it has to bar Operator-B's MTC devices in category a) while serves normally Operator-A's MTC devices in category b). Such a scenario is described in CR 178 to 3GPP TS 22.011.
For Access Class Barring in LTE system, SIB broadcasts barring related parameters are as according to FIG. 10.
According to 3GPP TS 22.011 V11.0.0, section 4.3.1, for access class barring the UE determines the barring status with the information provided from the serving network, and performs the access attempt accordingly. The UE draws a uniform random number between 0 and 1 when initiating connection establishment and compares with the current barring rate to determine whether it is barred or not. When the uniform random number is less than the current barring rate and the type of access attempt is indicated allowed, then the access attempt is allowed; otherwise, the access attempt is not allowed. If the access attempt is not allowed, further access attempts of the same type are then barred for a time period that is calculated based on the ‘mean duration of access control’ provided by the network and the random number drawn by the UE.
Thus one could consider extending ACB parameters for EAB, as proposed in R2-113339 and R2-113217. Also for GERAN, some detailed solutions for EAB had been discussed in G2-110010, G2-110018, G2-110026.
However currently all access barring parameters in LTE are common to all PLMNs which share the RAN node. And none of the proposals clarifies how EAB should work in case of network sharing.
In UMTS, the concept of per-PLMN access class barring is present. The network may include a “Domain Specific Access Restriction For Shared Network” IE which includes one or several Domain Specific Access Restriction Parameters per PLMN in case of network sharing in SIB3. However, the “domain specific access Restriction” indicates whether the cell is barred or not for Access Class 0 up to Access class 15. That means the parameter indicates whether the cell is barred for UEs having a certain access class and having selected a certain PLMN. Thus, this concept would mix up the ideas of access class barring and EAB. Thus, the operator may not apply simultaneously access class barring to certain access classes and EAB to UEs of a certain roaming status reducing flexibility for the operator.